1. Field of the Invention
The present invention relates to a stencil printing machine which conveys a print medium while pressing the print medium to a drum on which a stencil sheet is mounted, and transfers ink oozing from perforations of the stencil sheet onto the print medium.
2. Description of Related Art
Printing method of a conventional stencil printing machine include an inner press printing method (refer to Japanese Patent Laid-Open Publication No. 7-132675) and an outer press printing method (refer to Japanese Patent Laid-Open Publication No. 2001-246828).
Brief description of the inner press printing method is as follows. As shown in FIG. 1, the conventional stencil printing machine with the inner press printing method has a drum 100 and a paper cylinder 101, which are rotatably provided and placed so that the outer peripheral surfaces thereof are partially close to each other. The outer peripheral surface of the drum 100 is provided with a sheet clamping portion 100a which clamps an end of a stencil sheet 104, and the outer peripheral wall thereof apart form the sheet clamping portion 100a is flexible and formed by an ink permeable screen 102.
An ink supply mechanism 105 is provided inside the drum 100. As shown in FIG. 2, this ink supply mechanism 105 has an inner press roller 106 which is an ink supply roller and is rotatably provided in a roller support member 107. The inner press roller 106 is constructed to be movable between a press position and a holding position. At the press position, a force is applied to the roller support member 107 in a direction shown by an arrow a in FIG. 2 so that the inner press roller 106 presses the inner peripheral surface of a screen 102. At the holding position, the roller support member 107 is rotated in a direction shown by an arrow b in FIG. 2 so that the inner press roller 106 is spaced apart from the inner peripheral surface of the screen 102. The inner press roller 106 is located in the press position while print paper 111 passes and comes to the holding position during the rest of the time. The inner press roller 106 also has a function to allow printing pressure to act on the inner peripheral surface of the screen 102.
Further, the roller support member 107 is rotatably supported about a support axis 108 serving as a center and provided with a doctor roller 109 and a driving rod 110. The doctor roller 109 is cylindrical and fixed by the roller support member 107 in the vicinity of the inner press roller 106. The driving rod 110 is rotatably supported by the roller support member 107 and placed in an upper space formed by the outer peripheral surfaces of the inner press roller 106 and the doctor roller 109 on the sides close each other. Ink 103 is supplied to this upper space from an unillustrated ink supply unit.
Next, the outline of a printing operation will be sequentially described. The stencil sheet 104 with a perforation image formed therein is mounted on the outer peripheral surface of the screen 102. Then, in a printing mode, the drum 100 and the paper cylinder 101 are rotated in synchronization with each other in a direction shown by an arrow in FIG. 1. Thereafter, the print paper 111 is fed between the drum 100 and the paper cylinder 101.
Once the print paper 111 is fed, the inner press roller 106 presses the screen 102 and rotates following the drum 100 while pressing the screen 102. The ink 103 that has passed through the gap between the doctor roller 109 and the inner press roller 106 is applied on the outer peripheral surface of the inner press roller 106, and the applied ink 103 is sequentially supplied onto the inner surface of the screen 102 by the rotation of the inner press roller 106.
Further, when the inner press roller 106 presses the screen 102, the screen 102 stretches out toward the outer periphery thereof by the pressure and comes into contact with the paper cylinder 101 under the pressure. Then, the print paper 111 that has been conveyed between the drum 100 and the paper cylinder 101 is conveyed between the inner press roller 106 and the paper cylinder 101 while being in contact with and pressed by the screen 102 and the stencil sheet 104. Due to this contact and pressure force, the ink 103 on the screen 102 is transferred onto the print paper 111 from the perforations of the stencil sheet 104, and thereby an ink image is printed on the print paper 111.
Brief description of the outer press printing method is as follows. As shown in FIG. 3, the conventional stencil printing machine with the outer press printing method has a drum 120. On the outer peripheral surface of the drum 120, a stencil sheet clamping portion 120a which clamps an end of the stencil sheet 104 is provided, and the outer peripheral wall 120b of the drum 120 apart from the stencil sheet clamping portion 120a is formed by a perforated ink penetratable member (ink permeable member).
An ink supply mechanism 125 is provided inside the drum 120. This ink supply system 125 has a rotatably supported squeegee roller 126 and a doctor roller 127 placed adjacent to this squeegee roller 126. Ink 128 is stored in an outer peripheral space surrounded by the squeegee roller 126 and the doctor roller 127. The ink 128 applied on the outer periphery of the rotating squeegee roller 126 passes through a gap between the squeegee roller 126 and the doctor roller 127. Thus, only the ink 128 with a predetermined thickness is applied on the squeegee roller 126, and the ink 128 having this predetermined thickness is supplied on the inner surface of the outer peripheral wall 120b of the drum 120.
Further, a pressure roller 130 is provided at a position facing the squeegee roller 126 and outside the drum 120. The pressure roller 130 is constructed to be able to move between a press position where the pressure roller 130 presses the outer peripheral wall 120b of the drum 120 and a holding position where the pressure roller 130 is spaced apart from the outer peripheral wall 120b of the drum 120. The pressure roller 130 comes to the press position while the print paper 111 passes and to the holding position during the rest of the time. The squeegee roller 126 is secured to a support portion which rotatably supports the outer peripheral wall 120b of the drum 120. There is a clearance between the outer peripheral surface of the squeegee roller 126 and the inner peripheral surface of the outer peripheral wall 120b of the drum 120 in the state where the drum 120 is not pressed by the pressure roller 130. When the outer peripheral wall 120b of the drum 120 is pressed by the pressure roller 130, the outer peripheral wall 120b of the drum 120 bends so that the inner peripheral surface of the outer peripheral wall 120b of the drum 120 comes into contact with the outer peripheral surface of the squeegee roller 126.
Next, the outline of a printing operation of the outer press printing method will be sequentially described. The stencil sheet 104 with a perforation image formed therein is mounted on the outer peripheral surface of the outer peripheral wall 120b of the drum. Then, in a printing mode, the outer peripheral wall 120b of the drum 120 is rotated in a direction shown by an arrow in FIG. 3, and the print paper 111 is fed between the drum 120 and the pressure roller 130.
Once the print paper 111 is fed, the pressure roller 130 presses the outer peripheral wall 120b of the drum 120, and the outer peripheral wall 120b is bent toward the inner periphery thereof. Due to this displacement, the outer peripheral wall 120b presses the squeegee roller 126, and the squeegee roller 126 rotates following the drum 120. The ink 128 that has passed through the gap between the doctor roller 127 and the squeegee roller 126 is applied on the outer peripheral surface of the squeegee roller 126, and this applied ink 128 is sequentially supplied onto the inner surface of the outer peripheral wall 120b by the rotation of the squeegee roller 126.
Further, when the pressure roller 130 presses the outer peripheral wall 120b of the drum 120, the print paper 111 which has been conveyed between the drum 120 and the pressure roller 130 is conveyed between the squeegee roller 126 and the pressure roller 130 while being in contact with and pressed by the stencil sheet 104. Due to this contact and pressure force, the ink 128 on the outer peripheral wall 120b is transferred onto the print paper 111 from the perforations of the stencil sheet 104, and thereby an ink image is printed on the print paper 111.
However, in the conventional stencil printing machines with the inner press printing method and the outer press printing method, ink pools are formed in the outer peripheral space between the inner press roller 106 and the doctor roller 109 and the outer peripheral space between the squeegee roller 126 and the doctor roller 127, respectively. Then, the ink 103 and the ink 128 of these ink pools are supplied to the screen 102 of the drum 100 and to the outer peripheral wall 120b of the drum 120, respectively. Therefore, when printing is not carried out for a long time, there has been a problem that the ink 103 and 128 stored in the ink pools are left contacting with the atmosphere for a long time, resulting in deterioration of the ink 103 and 128.
Further, since various rollers and the like for ink supply have to be arranged within the drums 100 and 120, there has been a problem that it is difficult to realize the small and lightweight drums 100 and 120.
The present invention was accomplished to resolve the above-mentioned problems, and an object of the present invention is to provide a stencil printing machine in which ink does not deteriorate even when printing is not carried out for a long time, and a small and lightweight drum can be realized.
The stencil printing machine according to the present invention has a drum, an ink supply device, and a pressure roller. The drum is rotatable and has a outer peripheral wall formed by an ink impermeable member. On the outer peripheral wall of the roller, a stencil sheet is mounted. The ink supply device has an ink supply unit at a printing position upstream of a maximum printing area of the outer peripheral wall of the drum and supplies ink on the surface on the outer peripheral wall from this ink supply unit. The pressure roller presses a fed print medium onto the outer peripheral wall.
In this stencil printing machine, when the print medium is fed while the outer peripheral wall of the drum is rotated and ink is supplied on the surface of the outer peripheral wall from the ink supply unit, the print medium is conveyed while being pressed by the pressure roller onto the stencil sheet and the outer peripheral wall of the drum. Meanwhile, the ink between the outer peripheral wall of the drum and the stencil sheet is diffused downstream of a printing direction while being squeezed by the pressing force of the pressure roller. At the same time, the diffused ink oozes from perforations of the stencil sheet and is transferred on the print medium, thus an ink image is printed on the print medium. The ink supplied on the drum is held in an approximately sealed space between the outer peripheral wall of the drum and the stencil sheet. Therefore, contact with the atmosphere is minimized, and it is not required to arrange various rollers for ink supply within the drum.
In a preferred example, ink leakage preventing grooves are provided on the outer peripheral wall at the positions outside the maximum printing area and covered by the stencil sheet. In this stencil printing machine, when the ink between the outer peripheral wall and the stencil sheet leaks outside of the maximum printing area, the leaking ink goes into the ink leakage preventing grooves.
The ink leakage preventing grooves are respectively provided at the right and left positions outside the maximum printing area in a printing perpendicular direction. In this stencil printing machine, the ink leaking from the maximum printing area of the outer peripheral wall in the printing perpendicular direction goes into the ink leakage preventing grooves.
The ink leakage preventing groove may be provided at a printing position downstream of the maximum printing area. In this stencil printing machine, the ink leaking in a printing direction downstream of the maximum printing area of the outer peripheral wall goes into the ink leakage preventing groove.
The ink leakage prevention groove may be provided on right and left outsides of the maximum printing area in a printing perpendicular direction and on a printing position downstream of the maximum printing area. In this stencil printing machine, the ink leaking from the maximum printing area of the outer peripheral wall in the printing perpendicular direction and the ink leaking in a printing direction downstream of the maximum printing area of the outer peripheral wall goes into the ink leakage preventing grooves.
The ink leakage preventing groove may be provided at a printing position further upstream of the ink supply unit upstream of the maximum printing area. In this stencil printing machine, the ink leaking in a printing direction upstream of the ink supply unit of the outer peripheral wall goes into the ink leakage preventing groove.
A plurality of the ink leakage preventing grooves may be provided. In this stencil printing machine, when the ink overflows from the ink leakage preventing groove on the inner peripheral side, the overflowing ink goes into the ink leakage preventing groove on the outer peripheral side. Further, in the case of forming the plurality of ink leakage preventing grooves whose total volume is the same as that of one ink leakage preventing groove, each of the ink leakage preventing grooves is formed to have a narrow width.
An Ink recovery device may be provided for recovering the ink flown outside the maximum printing area of the outer peripheral wall. In this stencil printing machine, the excessive ink is removed from the outer peripheral wall and recycling of the ink is achieved.
The ink recovery device may have an ink recovery groove at a printing position downstream of the maximum printing area of the outer peripheral wall and recover the ink stored in the ink recovery groove. In this stencil printing machine, the ink flown out on the downstream side of printing by being squeezed by the pressure roller is removed from the outer peripheral wall, and recycling of the ink can be realized.
In the ink recovery groove, a depression preventing member can be placed through which the ink can pass. In this stencil printing machine, the stencil sheet is not depressed into the ink recovery groove. Moreover, the stencil sheet does not stick to an edge of the ink recovery groove and thus does not seal the ink at the sticking position. Therefore, the ink smoothly flows into the ink recovery groove by being squeezed by the pressure roller. Furthermore, the stencil sheet is not depressed into the ink recovery groove when the pressure roller passes over the ink recovery groove.
The depression preventing member may be flush with the peripheral surface of the outer peripheral wall. In this stencil printing machine, the pressure roller moves over an approximately single circumference.
The ink recovery device may recover the ink stored in the ink leakage preventing groove by utilizing the ink leakage preventing groove as the ink recovery groove. In this stencil printing machine, the ink stored in the ink leakage preventing groove is certainly removed.
The ink supply unit may be provided along the printing perpendicular direction on the outer peripheral wall and supplies the ink almost uniformly in the printing perpendicular direction. In this stencil printing machine, the ink is diffused without unevenness in the printing perpendicular direction when the ink is diffused downstream in the printing direction by the pressing force of the pressure roller.
The ink supply unit may supply the ink from a plurality of ink supply ports provided at an interval in the perpendicular direction of printing on the outer peripheral wall. In this stencil printing machine, the stencil sheet is not depressed into the ink supply ports when the pressure roller passes over the ink supply ports.
The stencil printing machine may include ink volume adjusting means which controls a supply volume of the ink from the ink supply unit in the printing perpendicular direction, and control the ink volume adjusting means depending on a perforation percentage of the stencil sheet.
In this stencil printing machine, an ink supply volume is increased in an area with a high perforation percentage and decreased in an area with a low perforation percentage. Thus, only a required volume of ink is supplied in a required area.
The stencil printing machine may include the ink volume adjusting means which controls an ink supply volume from the ink supply unit in the printing perpendicular direction and control the ink volume adjusting means depending on a size of the print medium to be fed.
In this stencil printing machine, the ink is supplied to the area here the print medium is present, and the ink is not supplied to the are a where the print medium is not present. Thus, the ink can be supplied only to the required area.
The ink supply device and the ink recovery device may be always driven in the printing mode. In this stencil printing machine, in the printing mode, the ink is continuously supplied to the outer peripheral wall from the ink supply unit, and the ink that has flown into the ink leakage preventing groove from the outer peripheral wall is always recovered. Additionally, an adequate amount of ink is always held on the outer peripheral wall.
A width of the pressure roller may be set to a width between the ink leakage preventing grooves, respectively provided at the right and left positions in the printing perpendicular direction so that the pressure roller presses the inner sides of the respective outer edges of these two ink leakage preventing grooves. In this stencil printing machine, the pressure roller does not seal the ink leakage preventing grooves while pressing these grooves. In the case where the ink recovery device is constructed to recover the ink in the ink leakage preventing grooves by suction power, the pressure roller does not press the outer sides of the ink leakage preventing grooves.
In addition, in this description, the printing position upstream of the maximum printing area of the outer peripheral wall of the drum means the upstream area of the maximum printing area in the ink flowing direction on the outer peripheral wall of the drum at printing, and the printing downstream area means the downstream area of the maximum printing area in the ink flowing direction on the outer peripheral wall of the drum at printing.